1. Field of the Invention
The present invention relates to an impeller having such a blade surface shape that the blade surface of the impeller can be cut by a lateral surface of a rotating tool using a 4-axis machining machine having three linear axes and one rotation axis, and to a method of machining the impeller.
2. Description of the Related Art
FIG. 15 is a diagram illustrating an impeller having a conventional general blade. A blade surface 3 of an impeller 1 has a 3-dimensional shape formed of a surface made up of a plurality of line elements 2. Conventionally, when the impeller 1 is machined, the direction of the central axis of a tool (not illustrated) when a lateral line of the tool follows the line elements 2 that form the blade surface 3 of the impeller 1 is not taken into consideration.
Japanese Patent Application Laid-Open No. 61-109608 indicates that a blade has a 3-dimensional shape formed of n line elements, and the blade is machined by aligning the axis of an endmill in the direction of the line elements. However, the direction of the central axis of the endmill for aligning with the line element is not taken into consideration, and 5-axis control is required in order to align the central axis of the endmill with a first line element and the n-th line element.
Japanese Patent Application Laid-Open No. 8-254198 indicates that a main blade has a 3-dimensional shape formed of two line elements and the main element is machined by aligning the central axis of an endmill in the direction of the line elements. However, this technique does not take the direction of the central axis of the endmill for aligning the line elements into consideration. Due to this, 5-axis control is required in order to align the central axis of the endmill with the respective two line elements similarly to Japanese Patent Application Laid-Open No. 61-109608.
Japanese Utility Model Application Laid-Open No. 4-54997 indicates that an impeller of which the blade surface is made up of line elements is fixed in a tilted manner and is 3-axis machined. However, since the line elements that form the blade surface are parallel to each other, this technique relates to machining of an impeller having a simple blade surface shape obtained by bending a flat surface, capable of machining a workpiece without rotating the workpiece.
Japanese Patent Application Laid-Open No. 2010-269417 discloses a method of machining an impeller using 4-axis machining having a tilted rotation axis.
International Publication WO 91/03648 discloses machining of such a blade surface that line elements that form the blade surface are parallel to a plane perpendicular to a rotation axis. However, WO 91/03648 does not disclose machining of such a blade surface that line elements that form the blade surface cross a plane perpendicular to a rotation axis.
In order to efficiently cut the blade surface of the impeller in a short time, the blade surface is formed of line elements that can be machined by a lateral surface of a tool. If the line elements are skew to each other, when the blade is machined by a lateral surface of the tool in a state where the lateral line of the tool follows the line elements that form the blade surface, the tool axis is tilted. Thus, it is necessary to machine the blade using a 5-axis machining machine. Moreover, when such a blade is machined using a 4-axis machining machine, it is not possible to machine the blade by the lateral surface of the tool, but it is necessary to machine the blade by a tip end of the tool.